[Murph]

Il2 1946 includes everything that is in previous versions of the game and more. It is the required starting point for modding the game. I don't think any of the mods will work over just FB.
Il2 FB was an expansion pack for earlier versions of Il2, but was superceded by Ace Expansion Pack, Pacific Fighters and 1946. 1946 version 4.08 is the last official version, with 4.09 an official beta patch.